This invention relates to an Steel based Adamite roll which may improve its wear resistance and minimizes its surface roughness, as well as prevents defects such as surface roughness and defective dimensions of a steel rolled.
An Steel based Adamite roll finds a wide use as an intermedite roll in a rolling mill, because of its properties which provide a compromise between those of a cast steel roll and a cast iron roll.
It is known that a roll causes the surface roughness and defective dimensions in a steel rolled due to wear and seizure in the surface of the roll, thus dictating an intermediate re-assembly or replacement of rolls, with the resulting lowering in efficiency in rolling operation.
The typical composition of an Steel based Adamite roll of the prior art is shown in Table 1. However, to meet requirements, as the case may be, such as, for the types, configurations of rolled products, there are many variations in the chemical compositions of the rolls or rolling operation, such as by increasing the content of carbon, adding Cr, Mo and Ni, modifying the processes of casting and heat treatment of the rolls, or by adjusting the cooling rate of a roll, the screw-down setting and the rolling load, thereby attaining improvements in the rolling efficiency.
Table 1 ______________________________________ C Si Mn Ni ______________________________________ 1.4 to 1.7 % 0.5 to 0.7 % 0.5 to 0.7 % 0.5 to 1.0 % Cr Mo Fe Hardness (Shore) ______________________________________ 1.2 to 1.5 % 0.2 to 0.5 % Balance 45 to 50 ______________________________________
As those rolls are used at an intermediate stand for about one hour, then the temperatures at the surfaces of the rolls are increased and thus the roll surfaces are covered with thin scales. This condition is most suitable for rolling.
However, the prior art Steel based Adamite roll surfaces from disadvantages in that the surface temperature of a roll is extremely raised, when rolling the steels which require a high rolling load, steels which are hard to roll, because of contents of special elements, steels of a large size and a short rolling pitch or steels requiring a high rolling temperature. Thus, in the case of a high rolling load, surface scales are peeled off, causing seizure in such portions, which seizure in turn leads to excessive wear and eventually re-assembly or replacement of the roll. In the case of section steel, as well, the pass of a roll causes surface roughness and the resulting scale peeling and seizure in the portions of the roll surfaces which are subjected to the difference in the peripheral speed, resulting in impaired surface condition of steels rolled. In addition, if a roll having a high hardness at an elevated temperature and a high tensile strength is used, there also results peeling of scales and seizure, if such a roll has a tendency to cause peeling. The surface of scales contains Fe.sub.3 O.sub.4 in a small amount, while the internal portion of scales consists mostly of FeO which is soft and presents low mechanical strength. With the progress of oxidation, the amount of FeO is increased, causing internal cracking and pores, thus accelerating peeling. As a result, the more insusceptible to the oxidation, the finer the scales which are insusceptible to peeling.